Conventionally, there is known a vane pump 1 as shown in FIG. 5A, which includes a rotor chamber 2, a rotor 3 eccentrically accommodated in the rotor chamber 2 and a plurality of vanes 4 attached to the rotor 3 for making sliding contact with an inner peripheral surface 2a of the rotor chamber 2 at their leading ends. As the rotor 3 is rotatably driven in the vane pump 1, working compartments 5 surrounded by inner surfaces of the rotor chamber 2, an outer peripheral surface 3a of the rotor 3 and the vanes 4 undergo a volume change and a working fluid drawn into the working compartments 5 from an inlet port 6 is discharged through an outlet port 7.
In such a vane pump 1, if the thrust surfaces of the rotor 3 and the inner surfaces of the rotor chamber 2 arranged in a mutually facing relationship are brought into surface-to-surface contact with each other over the nearly whole surfaces thereof as illustrated in FIG. 5B, an increased resistance against sliding movement is generated, thereby reducing rotation efficiency of the rotor 3. In contrast, if gaps “S” are left as illustrated in FIG. 5C to avoid direct contact between the thrust surfaces of the rotor 3 and the inner surfaces of the rotor chamber 2 arranged in a mutually facing relationship (see, e.g., Japanese Utility Model Laid-Open Application No. 58-189388 and 62-179382), a problem is posed in that the working fluid in the working compartments 5 is leaked through the gaps “S” according to a change in internal pressure.